In both wet-lay and air-lay operations, fibrous webs are formed by depositing fibers from a fluid stream onto a foraminous forming surface. In commercial installations, it is highly desirable to increase product output to thereby minimize the unit cost of manufacturing, and this is particularly important when manufacturing single and limited use fibrous products, such as cosmetic pads, industrial towels, household towels, facial tissues, impregnated wipes, components of disposable diapers and sanitary napkins, etc. These products must be economically manufactured so that they can be sold profitably at a price that is low enough to justify their frequent disposal.
One way of increasing production output in a web forming line is to form the fibrous web several times wider than that of the final product, and thereafter sever the web in laterally spaced-apart regions to form several web sections from which the product can be formed. This techinque can be very advantageously employed in the formation of single and limited use air-lay products that are intended to compete with products made by faster, wet-lay processes.
One approach to forming wide webs is disclosed and claimed in U.S. Pat. No. 4,065,832, issued to Rudolf Neuenschwander, and assigned to Scott Paper Company. The preferred apparatus disclosed in this patent includes a foraminous forming surface obliquely oriented to the direction of fiber flow through a conveying duct and intercepting the downstream end of said duct, whereby the lateral dimension of the foraminous surface between laterally spaced-apart duct sidewalls is greater than the width of the duct at its open downstream end, as measured in a direction generally normal to the direction of fiber flow through the duct. This oblique orientation establishes an acute angle .alpha. between one of the duct sidewalls and the forming run of the foraminous member, as is clearly shown in FIG. 1. This angular relationship provides a restriction adjacent the edge of the forming surface to cause the formation of a thin edge; especially in thick web structures. If the thin edge is not tolerable in the finished product it must be removed from the formed web; thereby resulting in production inefficiency. Thus, the apparatus disclosed in the U.S. Pat. No. 4,065,832 is not sufficiently versatile to form webs with a substantially uniform thickness from edge to edge over a wide range of basis weights.